This proposal represents a part of a collaborative research project planned by Dr. Craig Heller at Stanford University and myself at UC Santa Cruz. The hypothesis to be investigated is that sleep, shallow torpor, and hibernation are homologous physiological phenomena, all intimately related to thermoregulatory functions. The major objectives of the work described in this proposal will be: (a) to investigate the thermoregulatory adjustments and metabolic changes during the electrophysiological states of sleep in humans exposed to different ambient temperatures, and (b) to determine whether shallow torpor and hibernation represent an extension of thermoregulatory adjustments normally occurring during sleep states. Specific studies will be conducted to determine: (1) Changes in metabolism, va somotor tone, and skin and core temperatures during stages of sleep at a thermoneutral temperature. (2) How the stages of sleep and thermoregulatory mechanisms are influenced by ambient temperatures above and below thermoneutrality. (3) Whether hibernators or animals showing shallow torpor enter those conditions through sleep, and if so, whether thermoregulatory adjustments during entrance correlate with changes in sleep states, and (4) Whether hibernating animals exhibit seasonal variations in total amount and/or percentages of stages of sleep. We believe that this collaborative research should yield new insights into the interrelations between sleep, torpor, hibernation and thermoregulation and about the evolution and biological functions of sleep.